The principal objective of this proposal is to isolate, purify and chemically characterize the proteins involved in the biosynthesis, degradation and function of cyclic 3', 5'-mononucleotides in eukaryotes. Efforts will be made to isolate the adrenergic receptor from the membrane of the frog erythrocyte and to determine its relationship to adenyl cyclase and to the developmental changes in hormone sensitivity that occurs during amphibian metamorphosis. The multiple cyclic nucleotide phosphodiesterases of bovine cardiac muscle, frog erythrocytes and hamster insulinoma will be characterized and their molecular structure and regulatory properties will be determined, with particular emphasis placed upon the role of these enzymes in controlling intracellular levels of cyclic nucleotides. Cyclic nucleotide-dependent protein kinases will also be isolated from these tissues. Their endogenous substrates will be sought and the molecular forms which they assume during various physiological states, investigated. Analysis of each step in cyclic nucleotide synthesis and function may permit a rational approach to therapeutic manipulation of the diverse biological effects of cyclic nucleotides.